1. Field of the Invention
The present invention relates generally to transmission of radio frequency (RF) signal waves and specifically to the combination of different RF signal waves of various frequencies into a common transmission line, such as a waveguide, for application to a common propagating device such as an antenna for further transmission of the electromagnetic wave.
2. Background and Related Art
In electronic apparatus concerned with amplification and transmission of electromagnetic energy, the energy is usually transferred from one component of the system to another in the form of current through electrical conductors such as wire or cable. At very high frequencies and high power, the transfer of electrical energy through current carrying conductors becomes inefficient and impractical. Instead of transferring electrical energy as current through conductors, the high frequency high power energy can be transmitted by electromagnetic waves constrained within a guiding structure or waveguide. The transmission of energy by waveguide is carried out by radiating the energy, in the form of electromagnetic waves, into the inside of the waveguide structure through various coupling mechanisms such as probes, loops, crossbars and the like. This same energy may be extracted from the waveguide by a similar coupling mechanism at another location on the waveguide.
Many applications exist where it is desired to combine signals of various frequencies into a common transmission line structure. One example of such an application is in the field of microwave communications. One requirement of such combination is that the different signals must not improperly interfere with each other.
In this regard, various tuned filtering devices have been used in the prior art. However, due to the non-ideal nature of such devices, unwanted distortions and losses are inevitably introduced into the frequency bands of the different signals, causing the signals to be degraded in quality.
One particular application for combining electromagnetic signal waves has arisen with the advent of digital television (DTV). Broadcasters who wish to provide DTV service still must provide broadcast signals in the conventional NTSC (National Television Systems Committee) format to accommodate viewers with conventional NTSC television receivers. Absent a feasible and efficient way to combine the DTV signal and the NTSC signal for transmission by a common broadcast antenna (possibly on adjacent frequency channels) without causing unacceptable interference, interaction and distortion of the signals, this will require some broadcasters to build additional antennae and towers to carry their DTV signals. This represents a very expensive and undesirable proposition.
Accordingly, there exists a need in the art to enable the combination of multiple signals of different frequencies without mutual interference and distortion.